In general, a pipe joint is detachable from a fluid pipe in order to easily execute replacement and repair of the fluid pipe. Pipe joints have various structures according to uses thereof.
For example, in a refrigerating cycle apparatus such as an air conditioner in which a refrigerant flows into a fluid pipe, a flare type pipe joint has been conventionally used. However, in recent years, in order to protect the global environment, as refrigerants of refrigerating cycle apparatuses have been switched from a conventional chlorofluorocarbon refrigerant to hydrocarbon (HC) refrigerants such as combustible propane, ethane, ethylene, n-pentane, n-butane, and isobutane or a natural refrigerant such as carbon dioxide used under a high pressure, a bite type pipe joint having a refrigerant leakage amount less than that of the flare type pipe joint and conventionally used for coupling of a steel pipe for conducting a high pressure fluid has been in the tendency to be used. Such a kind of bite type pipe joint is described in, for example, Patent Document 1 and Patent Document 2. The refrigerating cycle apparatuses include all kinds of apparatuses operated by a refrigerating cycle, for example, an air conditioner, a dehumidifier, a heat pump type hot-water supply apparatus, a refrigerator, a freezing apparatus, and a cooling apparatus for a manufacturing process.
FIGS. 26 and 27 show a bite type pipe joint described in Patent Document 1. As shown in FIGS. 26 and 27, the bite type pipe joint includes a joint main body 201, a fastening nut 202 as a fastening member, and a tubular bite type sleeve 203.
The joint main body 201 has a pipe coupling port 211 into which a distal end portion of a coupling pipe 204 is inserted. An external thread 212 is formed on an outer circumferential surface of the joint main body 201. A guide tapered surface 213 is formed in an opening end portion of the pipe coupling port 211. When the bite type sleeve 203 is pressed toward the pipe coupling port 211, an end portion (i.e. a front end portion 203a) of the bite type sleeve 203 that is adjacent to the joint main body 201 is guided toward a central axis of the coupling pipe 204 by the guide tapered surface 213.
The fastening nut 202 has a through hole 222 into which the coupling pipe 204 is inserted. A pressing tapered surface 223 for pressing an end portion (i.e. a rear end portion) of the bite type sleeve 203 that is adjacent to the fastening nut 202 is provided around the through hole 222. An internal thread 225 for being screwed onto the external thread 212 of the joint main body 201 is provided in an inner circumferential surface of the fastening nut 202.
The bite type sleeve 203 is disposed between the joint main body 201 and the fastening nut 202. The bite type sleeve 203 has a through hole 231 into which the coupling pipe 204 is inserted. The cross-sectional shape of the bite type sleeve 203 along the axis is substantially a rectangular shape formed long in the axial direction, as shown in FIG. 26. A pressure receiving tapered surface 232 contacting the pressing tapered surface 223 is formed in a rear end portion of the bite type sleeve 203. An axial pressing force from the fastening nut 202 acts on the pressure receiving tapered surface 232. A front end portion 203a of the bite type sleeve 203 can contact the guide tapered surface 213.
An assembling process of the bite type pipe joint having such a configuration is performed as follows. That is, first, the distal end portion of the coupling pipe 204 is inserted into the through hole 222 of the fastening nut 202 and the through hole 231 of the bite type sleeve 203, and the fastening nut 202 and the bite type sleeve 203 are assembled in the coupling pipe 204. Next, the distal end portion of the coupling pipe 204 is inserted into the pipe coupling port 211. At this time, the front end portion 203a of the bite type sleeve 203 is disposed to face the guide tapered surface 213 of the joint main body 201. Next, the internal thread 225 of the fastening nut 202 is screwed onto the external thread 212 of the joint main body 201, and the fastening nut 202 is fastened to the joint main body 201 with a predetermined torque using a fastening tool. Thereby, when the fastening nut 202 is fastened to the joint main body 201, the front end portion 203a of the bite type sleeve 203 is pressed on the guide tapered surface 213 by the fastening nut 202. The front end portion 203a of the bite type sleeve 203 is then pressed and bent toward a central axis of the coupling pipe 204 by the guide tapered surface 213. As a result, since the front end portion 203a bites into the coupling pipe 204, the coupling pipe 204 is prevented from being separated from the bite type sleeve 203 and space between the bite type sleeve 203 and the coupling pipe 204 is sealed. Further, since the front end portion 203a of the bite type sleeve 203 is pressed on the guide tapered surface 213, space between the bite type sleeve 203 and the joint main body 201 is also sealed. Accordingly, the bite type pipe joint exhibits a high sealing performance. FIG. 27 shows a state where the fastening nut 202 is fastened to the joint main body 201.
In the conventional bite type pipe joint, in a state where the distal end portion of the coupling pipe 204 is not inserted up to an innermost portion of the pipe coupling port 211, i.e. in a state where a gap L exists between a distal end surface of the coupling pipe 204 and the innermost portion of the pipe coupling port 211, the fastening nut 202 may be fastened to the joint main body 201. In this case, when the fastening nut 202 is fastened to the joint main body 201, the front end portion 203a of the bite type sleeve 203 is pressed and bent toward the central axis of the coupling pipe 204 and bites into the coupling pipe 204 and thus the coupling pipe 204 moves to a direction indicated by a blank arrow A of FIG. 26. Accordingly, since the front end portion 203a of the bite type sleeve 203 does not sufficiently bite into the coupling pipe 204, sealing performance may be insufficient in a portion coupled to the coupling pipe 204. This problem may also occur in a pipe joint used in apparatuses other than a refrigerating cycle apparatus such as an air conditioner.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-74768    Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-36947